Conventionally, a domestic application of single-conductor full-duplex two-way communication is proposed. FIG. 10 is a conceptual diagram illustrating a domestic application example of the single-conductor full-duplex two-way communication. In this application example, electronic appliances such as a TV and a PC are connected with each other by an optical fiber 10 usable for the single-conductor full-duplex two-way communication, thus establishing a domestic multimedia network. The domestic multimedia network is connected with an outer network via a gateway and the like.
Digital broadcasting started in the fiscal year 2000. In a few years, it will become commonplace that a household is connected via FTTH (Fiber To The Home). In order to conform to the FTTH, the optical fiber of the household needs to have a transmission capacity of 100 Mbps at maximum. Approximately the same capacity is required for conforming to the digital broadcasting. Moreover, communication through network-type game machines and digital video editing machines will also be performed via the optical fiber of the household.
In order to realize such communication principally for high-definition video transmission, domestic communication requires a low-error-rate, high-quality transmission method with a transmission capacity of several-hundred Mbps.
As one such communication method, a domestic network by IEEE1394 is drawing attention. IEEE1394 supports a long-distance transmission and a very low error rate (lower than 10−12 in BER (Bit Error Rate)). Therefore, IEEE1394 is considered as an excellent method for the domestic multimedia network. As a medium of the long-distance transmission, a silica fiber and a POF (Plastic Optical Fiber) are considered. Especially, the POF is easy to use because the POF is easy to connect due to a large diameter thereof.
Incidentally, in order to realize the single-conductor full-duplex two-way communication, various proposals are made as to structures of members used for the single-conductor full-duplex two-way communication. For example, Japanese Publication for Unexamined Patent Publication, Tokukaihei 11-237535 (publication date: Aug. 31, 1999) (publication 1) discloses a structure of an optical sending and receiving device capable of preventing optical crosstalk that can occur while optical signals are being sent and received.
FIG. 11 is a perspective view illustrating a schematic arrangement of an optical sending and receiving device 100 disclosed in publication 1. The optical sending and receiving device 100 includes a laser light emitting source 101, an optical device 102, and a photodiode 103. The laser light emitting source 101 emits first signal light (laser light) s1. The optical device 102 causes the first signal light s1 to be incident into an end surface 111a of an optical fiber 111 in such a direction that is different from a direction in which second signal light s2 is emitted from the end surface 111a of the optical fiber 111. The photodiode 103 receives the second signal light s2 emitted from the end surface 111a of the optical fiber 111. The optical sending and receiving device 100 has such a structure in which the photodiode 103 is positioned out of reach of reflected light s3. The reflected light s3 is generated when the first signal light s1 incident into the end surface 111a of the optical fiber 111 is reflected by the end surface 111a of the optical fiber 111. With the foregoing structure, it is possible to prevent optical crosstalk of near-end reflected light noises.
Moreover, attempts are made to identify requirements on a ratio (optical crosstalk ratio) between received light and the optical crosstalk, the requirements being for attaining the long-distance transmission and the low error rate, which are supported by IEEE1394. For example, a model for optical crosstalk setting in case full-duplex two-way communication is performed via a single-conductor POF is disclosed in “OP i. LINK: Optical Transmission Technology to Connect 10 m by IEEE1394”, Nikkei Electronics, Dec. 4, 2000 edition (No. 784) (published on Dec. 4, 2000), pp. 167-176 (publication 2).
According to publication 2, in order to satisfy the requirement BER<10−12, it is necessary that an amplitude of the received light be 19 times higher than dispersion of a Gaussian noise. After simulations and experimental data analyses were conducted, it was found that an amplitude of the optical crosstalk needs to be equal to or lower than one-fourth of the amplitude of the received light, that is, the optical crosstalk ratio needs to be equal to or larger than 6.0 dB.
Incidentally, noises (optical crosstalk noises) in the single-conductor full-duplex two-way communication includes not only the optical crosstalk considered in publication 1 (optical crosstalk caused by near-end reflection), but also optical crosstalk caused by far-end reflection. Therefore, it is also necessary to suppress the optical crosstalk noises caused by the far-end reflection. This is an inherent problem of the single-conductor full-duplex two-way communication. If full-duplex two-way communication is performed via a double-conductor fiber, it is not necessary to consider this problem.
In publication 1, there is description of optical crosstalk of the first signal light s1 caused on the end surface of the optical fiber 111. However, optical crosstalk caused by reflected returning light generated on an emission end of the optical fiber 111 and in a sender-side module are not considered.
Therefore, with the art of publication 1, it is not always possible to lower the bit error rate to a desired range.
On the other hand, publication 2 describes the optical crosstalk caused by the reflected returning light generated on the emission end of the optical fiber 111 and in the sender-side module. However, in publication 2, an acceptable amount of optical crosstalk is set uniformly, even though there are various parameters.
Therefore, in order to manufacture an optical communication system according to conditions disclosed in publication 2, it is necessary to satisfy strict requirements in designing an optical system and the like of each member. As a result, a cost of the optical communication system increases.
The present invention was made in light of the foregoing problems. An object of the present invention is therefore to provide a method of manufacturing an optical communication system, the method being capable of increasing degree of freedom in manufacturing the optical communication system, thereby attaining a lower cost.